Shedding and seroprevalence of pathogenic Leptospira spp. in sheep and cattle at a New Zealand Abattoir.

ABSTRACT

A cross-sectional study was carried out on sheep and cattle slaughtered at a New Zealand abattoir from September to November 2010 to investigate the supplier-specific shedding rate, renal carriage rate and seroprevalence of leptospires. In the 2008/2009 season, this abattoir experienced three human leptospirosis cases from 20 staff, of which two were hospitalized. Urine, kidney and blood samples were collected from carcasses of 399 sheep (six suppliers, 17 slaughter lines) and 146 cattle (three suppliers, 22 slaughter lines). The urine and kidney samples were tested by quantitative real-time PCR (qPCR), while serum samples (from coagulated blood samples) were tested by microscopic agglutination test (MAT). In total, 27% (73/274; 95% CI 18-37) of urine samples tested positive by qPCR. Species-specific shedding rates (prevalence of positive urine qPCR) were 31% (95% CI 17-48) for sheep and 21% (95% CI 14-30) for cattle. For 545 kidney samples tested, 145 were qPCR positive (27%; 95% CI 17-39). The average prevalence of kidney qPCR positivity was 29% (95% CI 17-45) for sheep and 21% (95% CI 15-28) for cattle. Three hundred and thirty of 542 sampled sheep and cattle had antibodies against Leptospira borgpetersenii serovar Hardjobovis (Hardjobovis) and/or Leptospira interrogans serovar Pomona (Pomona), based on reciprocal MAT titre ≥1  48 (overall seroprevalence of 61%; 95% CI 48-73). Seroprevalence was 57% (95% CI 40-72) for sheep and 73% (95% CI 59-83) for cattle. Among the seropositive animals, 41% (70/170; 95% CI 30-54) were shedding (tested positive by urine qPCR) and 42% (137/330; 95% CI 30-54) had renal carriage (tested positive by kidney qPCR). Some risk management options for abattoirs or farms to prevent human leptospirosis infections include vaccination of maintenance hosts, the use of personal protective equipment, and the application of urine qPCR to detect shedding status of stock as surveillance and as an alert.